Feeds

GBEzine

Get a whole year of cutting-edge eco-building news and project reports for just £20.00 p.a. + VAT*

Built upon 30 years of experience, this fabulous new medium will feature inspiring and in-depth articles on eco-building projects from across the spectrum and from all over the UK, most of which are written by the very people that designed or built them.

Perfect for architects, builders, developers, self builders and anyone interested in keeping right up-to-date with green building trends and friends.

I know this has been covered somewhat before but would like some additional advice with regards our setup. We've just had our GSHP commissioned in the last few months and have been running the UFH for that time. So far all seems fine. Problem we have is with towel radiators in the bathrooms. The advice from Nu-Heat, the UFH providers, was to put the towel rails on the DHW circuit. Our plumber was dead against this and persuaded us to plumb them into the UFH circuit. He said they wouldn't get hot but warm enough to keep the towels warm. This would have been perfectly acceptable as they were never intended as a heat source. We haven't actually connected any towel rails to the system as yet as we're still at first fix stage on the electrics. Now that the weather has got colder, the heat pump is obviously working harder to keep the house warm. However the maximum temperature the UFH circuit is reaching is around 25 degrees and this keeps the whole house cozy. Hard to believe I know as I expected temperatures closer to 40. We're not living in the house yet, it hasn't been plastered and the MVHR system hasn't been switched on yet. In other words the house is losing more heat than it will when finally finished yet it is staying warm with UFH temperatures down in the 20s. The result is that the towel radiators would be virtually cold and not sufficient for warming butter never mind towels!!

So the question is do we alter the system and place the heated towel rails on the secondary return loop of the DHW system? Obviously this would mean sourcing specific towel rails for this purpose as you can't use standard ones. Think they must be brass or stainless steel. Has anyone else got their towel radiators on an UFH circuit? How do you find the temperature reached?

I think the plumbers concern with utilising the DHW circuit was wasted energy. However at present, the towel radiators would be useless with the flow temperatures we are getting. If they were on the secondary return loop, would they have to be thermostatically controlled with TRVs? I had intended putting electric elements in the rails as a backup in summer but if they are on the DHW circuit would this be a waste as you would always have DHW available year round?

No,no,no, do not connect your towel rads off the DHW primary side or the secondary for that matter as this will cause extended run times from the heat pump in hot water mode. You want the run time in HW to be as short as possible as the COP will be at it's wost when generating hot water; you don't want this load to be made MUCH larger by losing heat around the towel rads. I have experienced this set up and invariably the running costs become high.

Just one thing, if your MVHR is not yet switched on you may be loosing less, not more, heat than you will when you switch it on. Depends if you have windows open or not, and if plasterwork is doing the airtightness job.

On the plus side even a modest difference in temperature between towel rail with towel on and room makes a perceptible difference in comfort and drying speed.

Both the UFH manufacturer AND the heat pump supplier recommended NOT putting it on the UFH circuit! I understand the reasons for not putting it on the DHW side but this is what the manufacturers are recommending!

Yes we do need the towel rails. It's nice to have warm towels and the wife has insisted she wants them. Also the plumbing has been installed so I'm hardly likely to just not bother with them now!

Plasterboard is NOT doing the air tightness. The house is already very air tight even without the plasterboard. The intention is not to have windows open. However the chimney is still open as the log burner is not yet installed. Don't understand why the MVHR system would lose more heat. It would be extracting heat from the wet rooms and kitchen and redistributing that heat so how could it lose more?? It will also be extracting heat from the loft 'plant room' which has a large amount of heat producing electronics which are constantly producing heat, therefore there should always be warm air entering habitable rooms. From what I've been told from someone who runs a similar system it has reduced heat loss not increased it.

Sorry to digress from the main topic of the thread. Is your MVHR an energiVent Q Solar, or similar. Is the main fresh air intake in the loft? If so how will you achieve summer by-pass for cooler air in the summer? During my research into MVHR I came across the above system which is claimed to gain 3% from solar heat in the loft space. Having endured uncomfortable temperatures in a roof space installing MVHR ducts for one system I was curious how this could be overcome. Energivent told me that summer bypass could be arranged for external air but had not considered it necessary when I made my enquiries in 2009.

No it's an Itho unit. It has a summer bypass which means the unit simply extracts the warm air to outside without going through the heat exchanger. Relatively cooler air direct from outside is then distributed to the habital rooms.

Butter would be very soft at 25oC! No UFH but MVHR; we do use our downstairs wet room as a drying room from time to time. I deliberately had a large towel rail - 2m high x 600mm wide for 2+ large towels; works very well even when the C/H is off.

adh, I added the 2nd paragraph, above , on edit, while you were making your last comment. Very interested in your dilemma as I will file away the information for future reference in a new build and 2 extensive refurbs. I would put a lot of pressure on Nu-Heat to explain their advice and give you the evidence for it, but perhaps you have already done that? BTW, did you have a borehole or horizontal loop for the GSHP? Most of the comments about GSHP on GBF seem to involve boreholes; I hope costs could be reduced with ground trenches.

Posted By: adhDon't understand why the MVHR system would lose more heat

Sorry, maybe I wasn't clear, I meant if you are, as it seems, in our situation where the house isn't quite finished and still too dusty to put on the MVHR and it IS currently airtight then we'll loose more heat once we start ventilating it properly.

Having towel rads on the DHW with TVR (or even the programmable TVR I've seen on another thread) makes perfect sense to me, though as I said rads don't need to be that hot to warm/dry towels. BTW our heating flow temp is currently 33c, 1c outside (high of 5c. today.

b) Create a secondary loop off the DHW hot water cylinder. That will cause the GSHP to do more work but it should still use less electricity than a). Use a programmer and possibly a pipe stat on the return to control the pump. It doesn't need to run all the time the DHW is on.

Edit: You are right about special rads being needed - can't dose the DHW. Might also consider a mixer to drop the flow temperature if the towel rad is too hot.

Nu-Heat always recommend putting it on the DHW side. Their rationale is that they've designed their system for UFH output not additional towel rails. Whether that holds any truth I don't know. They also said the rails wouldn't get hot enough.

We put in a horizontal ground loop which is 300m long for the heat pump. Seems to be working fine at present but early days.

Understand the MVHR argument now and losing heat. I guess it will be marginal though taking the current state of the building into account. Interesting you're getting into the 30s on yours. Will check this morning on ours as it's 0 outside!

Thanks for all the advice. Seems like a bit of a dilemma. Putting it on the DHW side is less efficient but if you reduce the flow rate and temp to each rail how much less efficient than having it on the UFH side? Depends how much heat you actually take away from the DHW system in comparison to normal use. All food for thought.

Edit:Just checked in the house. UFH at 22degrees and outside air temperature here 0.2degrees. The towel rail supplies barely warm but it has perceptible heat!

We have a horse style towel rad and only the bit of the towel actually in contact with the rail feels significantly warm. I reckon you would need a pretty big flat rad to warm up towels properly - a heated cupboard of some sort might work better. Main benifit of a heated rail is the towels dry out reasonably quickly.

It's the increased drying time which I think is key. Towels hung on unheated rails take an age to dry but I guess with even a little warmth this time should decrease.

The heat pump is not pushing hot water out at 60 degrees. In fact it's set to output at 44 degrees which is more than adequate. Personally I feel it a waste to pump out water at 60 which is far too hot to shower in or use directly. Obviously the system must increase the temperature once a week which it does automatically to combate any legionella issues.

The issue with the UFH is the apparent low temperatures at present. You mention 35 degrees but so far I haven't seen anywhere near those temperatures in the system. This morning, and last night, with temperatures outside below zero, the UFH was still only at 23degrees. I can't see it ever reaching 35 except when it's very cold outside. With not living in the house yet it's hard to judge whether room temperatures are ideal but the house feels warm and comfortable.

Hmmmm,I was planning to switch the main/most used bathrooms radiator from its ground floor radiator supply (which is hardly ever on and wastes heat when it is on leastwise in the summer) to the pipework suppling boiler heat to the hot cylinder, so when the hot cylinder is heated this radiator, and this radiator alone, is heated as well.When i mentioned this to my brother,( who also has underfloor) he said that was exactly what his plumber had done and they were well pleased with the arrangment.I can only presume a recent development in response to (i) better insulation generally(ii) more underfloor being installedThe reason the ground floor radiator circuit is not used is cos the underfloor does most of the heating supplemented by the wood burner in the living room.The radiators are basically redundant.................except for the bathroom one.Dang!

I agree we don't need warm towels but it's not so much them being warm that's important. It's the drying time. Without additional heat they take ages to dry. This results in using more towels, more washing, and even more wasteful energy useage.

Also I'm not sure I agree with your assertion but that's a whole different topic....

<blockquote><cite>Posted By: orangemannot</cite>Hmmmm,I was planning to switch the main/most used bathrooms radiator from its ground floor radiator supply (which is hardly ever on and wastes heat when it is on leastwise in the summer) to the pipework suppling boiler heat to the hot cylinder, so when the hot cylinder is heated this radiator, and this radiator alone, is heated as well. </blockquote>

I don't know your heat pump set-up adh, but if the rad/UFH output is mixed down before UFH, it may be possible to tap in to that header before the mixer, meaning that your towel rail temp is not affected by the UFH 'required' temp (which will, for COP and economy purposes, be as low as poss), but will instead be at the output temps produced by the heat pump - which could be as high as 40-50C. Def in towel-warming territory. It may also be that the HP only gets as hot as the UFH min - 25 in which case disregard this suggestion and all who sail in her.

This may not comply with nu-heat's required installation pattern, (yaaawn) but neither would it be on the DHW side! Downside is, depending on set-up you may need a small pump. Laing, among others, do a mini-circulator with timer, just make sure it coincides with your heat-pump 'on times' by timing it or wiring it in sync with the heat-pump circulator.

Jonti - you have clearly never been married. Warm towels are not just de rigeur my boy, they are essential to the survival of the species, CO2 or no. This should be in your science text book, P42, paragraph 16b, subsection 12, subtitled: 'The meaning of Life'.

LizM - wahey - good old fashioned common sense. Never goes out of fashion in a crisis....

CwattersBah Humbug re rads being too hotNot physically possible as i cannot seem to be able to get the water any hotter than 85 deg centigrade, I like the smell off heat of a radiator, then I switch the circ pump off to save electric.PSWe do not have any eldery folk at present and any toddlers of our breeding should have more sense, otherwise they will learn....fast.PPSI believe it is an accepted fact that heat/burning is one of the first things a toddler learns, as i have never heard of one getting burned off a radiator, no matter how hot.PPPPPSOur 18 year old son recently revealed that his wee sister branded him with a red hot poker when they were 3/4/5 years of age ish. This poker had been heated in the wood burning stove.On reflection they made the sensible decision not to tell us at the time.cheersM

<blockquote><cite>Posted By: crusoe</cite>I don't know your heat pump set-up adh, but if the rad/UFH output is mixed down before UFH, it may be possible to tap in to that header before the mixer, meaning that your towel rail temp is not affected by the UFH 'required' temp (which will, for COP and economy purposes, be as low as poss), but will instead be at the output temps produced by the heat pump - which could be as high as 40-50C. Def in towel-warming territory. It may also be that the HP only gets as hot as the UFH min - 25 in which case disregard this suggestion and all who sail in her.

This may not comply with nu-heat's required installation pattern, (yaaawn) but neither would it be on the DHW side! Downside is, depending on set-up you may need a small pump. Laing, among others, do a mini-circulator with timer, just make sure it coincides with your heat-pump 'on times' by timing it or wiring it in sync with the heat-pump circulator.

Jonti - you have clearly never been married. Warm towels are not just de rigeur my boy, they are essential to the survival of the species, CO2 or no. This should be in your science text book, P42, paragraph 16b, subsection 12, subtitled: 'The meaning of Life'.

LizM - wahey - good old fashioned common sense. Never goes out of fashion in a crisis....<img title="" alt="" src="/forum114/extensions/Vanillacons/smilies/standard/devil.gif" complete="complete"></img></blockquote>

I hope no one minds me resurrecting this thread, but we have just had UFH installed in the 'granny annexe' attached to our house. The people who installed the UFH said we had to have a single radiator attached to the heating system (condensing combi boiler) and so we went for a towel radiator in the en-suite attached exactly as suggested by crusoe - i.e. before the manifold.

However we have a problem in that the towel radiator is really hot and is making the en-suite really hot and also the bedroom. Does anyone know if we can put a thermostatic valve onto this radiator and can anyone explain why we had to have a single radiator on the curcuit (something about pressure release was mentioned, but I have to admit that I had no idea what they were talking about!).

That need for a radiator sounds like proper cobblers ( to a reasonably proficient non plumber)(i) Unless it is leaking I cannot see how it could dissipate pressure???(ii) one should be able to "dump" more heat into the UFH circuit, than a radiator, so thats a scratch as well.(iii) The thermostacic valve question? It depends if the radiator is plumbed in series or in parralell i.e if it is on the same pipe run as the under floor = No, cos it will throttle the supply to the underfloor at the same time.I am not however up to speed on the idosyncracies of "combi boilers" but then some/not many plumber are either this from direct experience.gibbermuttertwitch